(a) Field of the Invention
This invention relates to novel crystalline titanoborosilicates and to their applications. More particularly, it relates to novel titanoborosilicate crystalline zeolitic materials possessing catalytic properties and to various conversion processes using such crystalline titanoborosilicates.
(b) Description of Prior Art
It has been demonstrated in the past that zeolitic materials, both natural and synthetic, and commonly referred to as molecular sieves, can have catalytic, sorption and separating properties. A number of existing processes such as catalytic cracking, methanol conversion, isomerization of xylenes, alkylation of aromatics, exemplify the use of these molecular sieve materials.
Typically represented by aluminosilicates, zeolites are structurally complex crystalline inorganic polymers based on an infinitely extending framework of AlO.sub.4 and SiO.sub.4 tetrahedra linked to each other by the sharing of oxygen atoms. This framework structure contains large and small cavities interconnected by channels. These cavities and channels which are generally uniform in size thus allowing selective adsorption of hydrocarbons, are occupied by cations and water molecules. The cations may be mobile and therefore can undergo ion exchange. In view of the mobility of the cations, it is believed that zeolitic materials are in fact solid electrolytes. The water molecules may be removed reversibly by the application of heat which in most cases effectively leaves intact a highly porous crystalline structure. As the ratio of SiO.sub.2 to Al.sub.2 O.sub.3 increases, the zeolitic material may become more hydrophobic. In addition to their adsorption properties, zeolites are utilized in certain catalytic processes.
In terms of composition, zeolites can be regarded as being derived from silica. The substitution of some of the silicon atoms within the crystalline framework of the silica by trivalent aluminum atoms generates an anionic site in the environments of the Al atoms so that, in order to preserve electroneutrality a cation such as that of the alkali metals or alkaline earth metals is required. Considering the fact that tetraco-ordinated aluminum atoms cannot share the same oxygen atom, it follows that y in the following emperical formula representing a typical zeolite cannot be less than 2: EQU M.sub.2/n O:Al.sub.2 O.sub.3 :ySiO.sub.2 :wH.sub.2 O
wherein n is the valence of the cation, Y is 2 or greater and w is a number representing the water contained in the intracrystalline channel systems of the zeolite after synthesis or crystallization in nature.
Prior art developments have resulted in the synthesis of more than 150 zeolite types. To date, forty zeolite minerals are known. Synthetic crystalline aluminosilicates are the most prevalent and are usually designated in the patent literature and in the published journals by symbols or letters. Examples of some of the synthetic aluminosilicate zeolites are:
Zeolite A (U.S. Pat. No. 2,882,243); PA1 Zeolite X (U.S. Pat. No. 2,882,244); PA1 Zeolite Y (U.S. Pat. No. 3,130,007); PA1 Zeolite ZSM-5 (U.S. Pat. No. 3,702,886); PA1 Zeolite ZSM-11 (U.S. Pat. No. 3,709,979); PA1 Zeolite ZSM-12 (U.S. Pat. No. 3,832,449); PA1 Zeta-1 (British Pat. No. 1,553,209). PA1 VS=very strong; PA1 S=strong; PA1 MS=medium strong; PA1 M=medium; PA1 MW=medium weak; PA1 W=weak; PA1 VW=very weak. PA1 (1) preparing a mixture consisting of the integral reaction products between a titanium-containing compound and an alkali tetrahydroborate, sodium silicate, an alkylammonium cation or a precursor of an alkylammonium cation, a mineralization agent such as sodium chloride and water. Oxides of silicon such as silicic acid and stabilized polymer of silicic acid (Ludox.TM. or Nalcoag.TM.) can also be used in place of sodium silicate, in which case, a hydroxide of an alkali metal or an alkaline earth metal or mixture thereof is used; PA1 (2) maintaining said mixture at suitable reaction conditions to effect formation of said titanoborosilicate, said reaction conditions preferably including a reaction temperature between 25.degree. C. to about 300.degree. C., a pressure of at least the vapour pressure of water at said reaction temperature, and a reaction time sufficient to effect crystallization of said titanoborosilicate.
U.S. Pat. No. 3,702,886 which is here considered relevant discloses the crystalline aluminosilicate ZSM-5 and the process of preparing the same. This patent shows the preparation of a crystalline aluminosilicate and a crystalline gallosilicate by reacting a silicon oxide with aluminum oxide or germanium oxide in a range of specific ratios under specified reaction conditions. The product obtained has a specified X-ray diffraction pattern. This patent is therefore limited to alumino or gallosilicates. Patents disclosing the synthesis of ZSM-11 and ZSM-12 are likewise limited in scope to crystalline alumino or gallosilicates which also provide specified X-ray diffraction patterns.
The production of the ZSM materials makes use of a mixed base system wherein sodium aluminate and a silicon-containing material are allowed to react in the presence of sodium hydroxide and an organic base template such as tetrapropylammonium hydroxide or tetrapropylammonium bromide under specified reaction conditions to yield the crystalline aluminosilicates.
U.S. Pat. No. 3,328,119 which is considered relevant art to this invention claims and teaches the process of preparation of a crystalline aluminosilicate wherein boria forms an integral part of the crystal framework structure of the zeolite material.
Another U.S. Pat. No. 4,269,813 which is considered relevant to this invention discloses a class of crystalline borosilicates designated AMS-1B and a process for preparing the same.
Additional relevant prior art comprises U.S. Pat. Nos. 3,329,480; 3,329,481; 4,029,716; 4,078,009; German Pat. No. 2,830,787. U.S. Pat. Nos. 3,329,480 and 3,329,481 relate to titanosilicates and zirconosilicates respectively. U.S. Pat. Nos. 4,029,716 and 4,078,009 relate to a crystalline aluminosilicate zeolite having a silica-to alumina ratio of at least 12 and a constraint index. ##EQU1## within the range of 1 to 12 and containing boron in an amount of at least 0.2 weight percent as a result of the reaction of the zeolite with a boron-containing compound.
German Pat. No. 2,830,789 relates to crystalline alumino, boro, arseno, and antimony silicates having specified X-ray diffraction patterns and to processes for preparing the same.